A typical gas turbine assembly has a plurality of rotor blades extending radially out from a turbine disk. These blades extend into the gas flow path. Each airfoil has a root supporting it from the disk. This is a fir tree or dovetail engagement with the disk.
The blade experiences periodic loading during rotation of the turbine rotor. This leads to blade deflection and vibration. As the frequency approaches the resonant frequency of the blade the deflection amplitude can increase to extreme limits. This produces high cyclical stresses in the blades. It is quite desirable to dampen the vibration to avoid high stress.
Each blade is independently installed along with its blade platform and the disk. Axially extending gaps exist between the platforms. Gas passing through this gap bypasses the blade resulting in a power loss, and also overheating of the support structure. Of course it is desirable to minimize such bypass.
Weight is also important in an aircraft gas turbine engine. This is particularly the case in a rotating part where the higher centrifugal force of the increased weight sets a requirement for heavier and stronger rotor disk.
It is therefore an object to dampen vibration and to seal leakage with a minimum weight friction damper. Centrifugal force acting on the damper weight establishes the load against the platforms which establishes the resisting friction force. The farther from the blade support the damper is, the higher not only the centrifugal force, but the greater the movement of the blade at the damper location. The damper is therefore more effective at this radially outward location.
The dampers are more effective if they are stiff in the circumferential direction. With the minscular movement occurring to dampen the friction, even slight differences such as changes in the cross sectional area of the damper are significant changes in stiffness.
Separate supports for the seal and damper would add weight with no damping or sealing benefit. The seal should be thin and conformable with the surface with the seal most needed in the high pressure difference areas.